My invention consists in cutting the inner or grinding surfaces of the mill plates into circular rows of teeth, concentric with the axis of the plate and projecting from the surfaces of the plates, so arranged that the teeth of one plate extend into the spaces between the rows of teeth of the other in combination with furrows in depth equal to the teeth and in lines running from the inner periphery outward technically termed " eight quarter dress " and also in combining with this arrangement of teeth on the plates a cone or cylinder of breaking teeth to prepare the grain, &c., &c., for the grinding teeth by which I increase very greatly the quantity of grinding surface in a mill of given size and enable it more effectually, uniformly and quickly to grind the substance under treatment.